This invention relates to a suspension system for a hermetically sealed motor-compressor unit.
The desirability of having an efficient suspension system for a hermetically sealed motor-compressor unit of the type particularly employed in a mechanical refrigeration unit is well known to those skilled in the art. Such suspension systems have two primary functions.
First, the suspension system is intended to isolate the internal compressor-motor unit from the shell which surrounds the same to prevent the transmission of noise to the shell and then from the shell to the outer environment. Secondly, the suspension system should be designed to prevent damage to the internal motor-compressor unit.
During normal operation of a motor-compressor unit, it is generally subjected to severe stress or mechanical shocks only during start-up of the machine. During start-up, the torsional forces generally produce angular or rotational movement of the motor-compressor unit in a direction about the vertical axis of the unit.
While the unit is being shipped from the manufacturer to its point of installation, the unit may also be subjected to severe stresses due to handling which will cause the unit to oscillate quite extensively in its shell making the various parts of the unit, such as the windings of the motor, the lubrication oil pump, and the discharge tube, subject to damage. Generally, the nature of the motion produced as a result of such handling is complex, resulting in the motor-compressor unit moving in a vertical direction or in an angular or rotational direction relative to the horizontal axis of the motor-compressor unit, or to a combination thereof. In either case, however, damage may occur to the various components of the unit unless such movement is significantly limited by the suspension system. In addition, the metal-to-metal contact resulting from such movement generally causes chips of metal to develop in the oil sump. Such chips might then become entrained in the oil with resulting damage to the lubricating system components and bearings.
Various types of suspension systems have heretofore been employed to effectively limit the movement of the motor compressor unit within the shell.
Generally, sets of springs are employed at or near the center of gravity of the mass defined by the motor-compressor unit to achieve optimum vibration isolation. Since the motor-compressor unit mass is supported at its plane of least motion, i.e. the center of gravity, some problems have occurred as a result of the impact between components, since excessive motion occurs at the extreme ends of the motor-compressor unit when the unit is moving in a generally angular direction relative to the horizontal plane of the unit. Typically, motion limiting means have been provided in strategic locations to prevent excessive motion at the extreme ends of the unit. An example of prior art suspension systems is disclosed in U.S. Pat. No. 3,689,207, wherein a cup-shaped member has a vertically extending foot movably positioned therein to prevent excessive movement of the unit in an angular direction relative to the horizontal plane of the unit.
Another suspension system heretofore commercially employed includes a bumper suitably attached to a vertical extension of the compressor shaft. A cup or similar member is provided in spaced relation to the bumper to prevent undesired excessive movement in an angular direction relative to the horizontal axis of the motor-compressor unit. This suspension system also includes springs to prevent excessive downward movement in a vertical direction. An elastomeric shock absorber is provided to prevent the starting torsional forces from producing metal-to-metal contact and subsequent high impact forces, between a connecting ring and anchoring bolts passing through holes provided therethrough.
The suspension system described hereinabove has proven to be effective; however, the system must permit wide fabricating and assembly tolerances to accommodate the various components of the suspension system which result in an excessive space allowance within the shell. By increasing the space within the shell, additional impact and rebound forces are generated which may increase the possibility of damage to the components of the motor-compressor unit causing a concurrent increase in reliability problems. In addition, the use of a separate bumper and associated cup have resulted in increased costs in manufacturing the unit.